Here is the text I will be putting on my www.astra16v.co.uk site when I next update it. Though I'd post it here in advance incase anyone is interested. It will be finished tomorrow, all I have to do is run it in and I'll be at the pod on the 14th.
September 2001 Engine Rebuild.
It is that time again where I just feel my car is not giving all it could. It felts tried and lifeless. The last rebuild was done just over two years ago and the car has done around 20,000 miles in that time and to be fair, the car has been given a little stick every now and then. Time for a spruce up I think. This engine rebuild was done with the generous help of David and Henryk Franczak who both have a good knowledge of Vauxhall C20XE and C20LET engines. I merely gave a helping hand with some of the jobs that were done, learning as I went.
What will be done with the engine?
There was nothing in particular wrong with the engine, it just felt like it was tired and it did not have the performance it used to have. The idea of this rebuild is to revitalise the engine by sourcing any problems and improving on existing modifications.
One place we intend to look out for most of all is the route of the airflow into the engine. I have not matched the inlet manifold to either the head or the throttle bodies, there is apparently a big gain in power to be had here. I have always suspected that the head modifications were not as good as they could have been, this was also to be checked and improved on if possible.
Since the engine was rebuilt two years ago it has smoked mildly on start-up. This is most likely down to worn oil stem seals, which will be replaced. Also in this area, the valve seats will be re-lapped and the valves will be polished to a mirror finish.
The bottom end will be checked for wear on the bores, crank journals and bearings. Any worn items will need to be replaced or reconditioned. I had suspected bad compression for quite a while now so the rings will also be checked. Before the engine came out I did a quick compression test. It indicated that all bore compressions were lower than they should be and number one cylinder was especially low.
Since the last rebuild I had regretted not fitting a lightened flywheel. After seeking advice I decided to go for SBD’s 5.4kg lightened and balance flywheel. This is 2kg lighter than the standard item and should make a very noticeable difference.
What was found upon disassembly?
As soon as the engine was out the inlet manifold was removed complete with throttle bodies still attached. Upon looking through them with the butterfly open, you could see a huge step from the throttle body to the inlet manifold. The step was from 2-3mm, thus reducing the overall diameter by 4-6mm, which is over 15% of the opening! The same step was there between the inlet manifold and the head. Straight away it looked as though an increase in power was going to be had.
Next up we looked into the head. I have to say that what I saw was very disappointing. The head looked as though it had been attacked with a bit of wet and dry and no real headwork appeared to have been done.
The head was removed and I saw my Omega pistons for the first time. Once these were removed we could see the bores and the rings. The bores appeared to be in very good condition, the hone marks were still visible in most areas. The rings on the other hand were worn, especially the top rings. They had worn so that they were almost half their thickness leaving a thicker lip around its protruding edge. The ring on piston number one was broken in two places, this explains the lower compression on this cylinder, the most likely reason for this ring breaking would be the fact that it had lost it’s strength due to being worn to half it’s thickness. The unusual wear would need investigation and all rings need replacing.
The crank was then removed and measured. We found that the crank journals were standard size and unworn. The main bearings were well within tolerance, but the big end bearings we only just within tolerance. It was decided that these would be replaced.
The valves were later removed from the head to reveal the triple angle valve seats, although there appeared to only be two angles on the inlet side. Also the tops of the seats appear to have been machined down to allow even more air in. The bottom of the valve guides have been truncated so that they were not in the air flow. The combustion chambers looked untouched. It appears that the head did have some good modifications to it, but I was still disappointed with the work carried out on the ports. The exhaust ports looked untouched.
We examined the valve seat to see that they were not in great condition, but nothing a good lapping couldn’t solve. All the uprated valve spring and titanium caps appeared to be fine.
The clutch was examined and appeared to be in almost new condition. This clutch was sold as an uprated item and appeared to be a standard item from Luk who are a European company. Luk make good clutches and I have to say that I was impressed with how mine performed. The part number was noted in order to save money on any future clutch purchases.
After a trip to SBD with the pistons and the rings, it was suggested that the wear on the rings was due to tiny particles of metal in the oil which had been trapped in between the piston ring gaps and the rings. This metal embedded itself into the alloy of the piston and the moving ring wore up against it. This would explain why the ring has worn, but the weaker material of the piston was completely intact. The ring gap will be cleaned out fully before assembly. It is anyone’s guess as to the origin of these tiny particles.
What was done to the engine?
First off the inlet manifold was attacked and smoothed. Loads of metal was removed from this area and the flow into the head was now much more direct. The whole inlet manifold was enlarged and hence the corresponding inlet ports on the head were also opened up. The size of these ports were now considerably larger than before and tapered down to match the standard size. The ports were cleaned and polished to a smooth finish and looked very impressive. The exhaust ports were enlarged slightly to the size of a standard gasket. The exhaust ports were also polished, as were the combustion chambers.
The valve were all polished to a mirror finish and lapped back into the head. The valve stem seals were replaced also. The pistons were cleaned and the new rings were fitted. The bottom end was re-honed and cleaned, the big end bearings replaced. Everything was rebuilt, all stretch bolts were replaced including the ARP uprated rod bolts. The new flywheel was fitted and the gearbox bolted on.
The finishing touches.
Once the engine was back in the car the engine was filled with a low-grade oil in order to run in the new components. For this I used Castrol 15W40 mineral oil for 500-800 miles before changing to Castrol GTX Magantec 15W40 Semi-synthetic. The gearbox fluid was drained and Duckhams fully synthetic 75W90 gearbox fluid was used instead. This stuff is suitable for the Quaife differential but would not be suitable for other limited slip deferentials that operate with clutch internals.
Post run-in results.
The car was rolling roaded 4 weeks before the rebuild, it got 197.5bhp. We are sure that the recondition work along got this up above 200bhp, and the extra work on the head and the inlets could add as much as another 20bhp. We are hoping to see around 220bhp next time the car is on the rollers and an improved time at SantaPod, hopefully in the 13s. There will be an update here soon as to any improvements.
There are plans for the future. Now that the engine is almost complete there are just a few components that I’d like to finish it off. Unfortunately these components are expensive, regardless, I will have them fitted over the next few months.
Firstly I would like to have the MBE ECU upgraded to the new software version. This would enable me to use the wide range lambda probe to its full capacity. This combined with a quick remap should make use of the recent air flow increase and will hopefully get the system to fuel correctly at all times.
Secondly I would like to fit the SBD manifold as this is very different to the one I currently have. I feel that my manifold may well be the culprit for the two major flat spots that I have. This should finish off the engine nicely for now. There are more ideas flying around, but for the time this car is my primary form of transport, so for now it is staying sensible (?)
I will be looking out for a catch tank as the current system is open to the elements and I suspect that the engine is experiencing condensation on the inside when left over night. This causes the large amount of fumes from the crank case for the first few miles of driving. A catch tank would catch any fluid and hopefully reduce the condensation inside the engine.
The current bonnet will be sold and a non GTE item will replace it. The side vents will be replaced with recessed louvres in the same outline shape as the original GTE vents. Above the throttle bodies there will be loads of vents allowing air straight onto the air filter. This will hopefully reduce in induction temperature and help gain a few extra bhp.
Other plans for the engine include cosmetic changes. I plan to anodise the cam cover and cam belt cover, paint the strut braces to match, fit coloured silicon hoses and give the engine bay a good clean. The overall plan is to make it look like a different engine bay and to also make it pull a crowd as there is nothing more annoying than having a heavily modified engine that nobody notices.